1. Field of the Invention
The invention relates to a vacuum-tube picture screen device with a stand-by function according to the preamble of claim 1.
2. Description of the Related Art
In the switched-on state, vacuum-tube picture screen devices such as, for example data display devices, convert energy into waste heat in pauses between applications. Moreover, the end of the service life of the picture tube is rapidly reached with continuous operation and the predictable average fault-free operating time of the deflection device only achieves low values.
In order to avoid these disadvantages, it has previously been proposed to switch off the video signal and to allow the picture tube heater and the deflection device to continue to run as in normal operation. Although this reduces the beam power of the picture tube while still providing an instant-on function, the risk of cathode poisoning remains.
In another implementation, only the picture tube heater is maintained, which results in a significant power reduction while still providing an instant-on function. However, there is the risk of cathode poisoning.
Furthermore, there is the possibility of switching off the line voltage. The power reduction is then 100%. However, the instant-on function is no longer provided. In addition, frequent switching-on and off of the vacuum-tube picture screen device puts the heating cathode at risk.
The possibility is also known of allowing the vacuum-tube picture screen device to continue to run for a predetermined time interval, then to switch off the video signal and also to switch off the line voltage after a further predetermined time interval. The power reduction and the instantaneous-picture function then depend on the application profile. A disadvantageous application profile, however, can again put the heating cathode at risk.
From IBM Technical Disclosure Bulletin, Vol. 34, No. 9, February 1992, Armonk (US), pages 281 to 283, measures for increasing the service life and the fault-tolerance of a vacuum-tube picture screen device are known. The measures include the complete or partial switching off of the vacuum-tube picture screen device whilst completely or partially maintaining the cathode heating. In an additional possible embodiment, it is proposed to apply to one of the grid electrodes a bias voltage which is selected in such a manner that a beam current is stopped. Although these measures contribute to the reduction in the power losses in the stand-by position and thus to the protection of components while providing an instant-on function, they do not prevent cathode poisoning from occurring. This can therefore occur because it has not been assured in any of the cases that an electron cloud which was generated due to the cathode heating and to an indeterminate video signal that continues to pend is drawn off at the cathode.
From published German Patent Applications 36 06 736 A1 and DE 23 22 875 B2, measures for reducing the filament voltage of the picture tube of a vacuum-tube picture screen device in a stand-by mode are known which, however, do not solve the problems in vacuum-tube picture screen devices in stand-by mode as described initially.
From the German Published Application 26 24 965 A1, a switched-mode power supply for a television receiver is known which is especially constructed for generating an auxiliary operating voltage. However, the problems in vacuum-tube picture screen devices in stand-by mode as described initially are not solved by this switched-mode power supply, either.